1. Field of the Invention
The present invention relates to a toner for electrophotography, a developer using the same, and an image forming method and a process cartridge using this developer.
2. Description of the Related Art
Depletion of petroleum resources and a problem of global warming by carbon dioxide discharged into the atmosphere due to mass consumption of the petroleum resources are concerned. There, when a binder resin used for a toner is replaced by a plant-derived resin, carbon dioxide generated from the binder resin circulates only in the environment, and there is a possibility that the problem of global warming and the depletion of the petroleum resources may be simultaneously solved. Also, another effort for the environmental problems, an energy-saving copying machine is desired. Most of the energy consumed by a copying machine is thermal energy for melting a toner and fixing it on paper. Thus, an energy-saving copying machine with reduced environmental load may be achieved if the toner melts at a low temperature, and a low-temperature fixing toner is desired. As a means for obtaining the low-temperature fixing toner, a glass transition temperature of a binder resin is reduced, in general. However, when the glass transition temperature is excessively reduced, storage stability of the toner degrades. As a means to achieve both storage stability and low-temperature fixing property, it is known to use a crystalline resin as a binder resin. However, a high ratio of the crystalline resin in the binder resin degrades dispersibility of a pigment, and there is a problem that color reproducibility of a fixed image degrades.
In addition, a high degree of crystallinity of the crystalline resin causes a problem that the pigment does not easily penetrate into the binder resin. Because of this, the pigment is located eccentrically in toner particles. The pigment does not spread when an image is formed with the toner and fixed on paper, and as a result, the image has low color reproducibility. As a countermeasure, it is known to use a masterbatch that a pigment is dispersed in a resin in advance. However, when the crystalline resin is used for the masterbatch, the pigment still does not disperse well in the resin. It is possible to disperse the pigment well when a non-crystalline resin is used for the masterbatch, but it is a factor of inhibiting low-temperature fixing property derived from the crystalline resin.
Accordingly, a toner including crystalline resin and having excellent color reproducibility, low-temperature fixing property and storage stability, and a related technology thereof have not yet been obtained, and at present, further improvement and development therefor are desired.
As a technology close to the present invention, in Japanese Patent Application Laid-Open (JP-A) No. 2010-77419, a crystalline resin is used for the purpose of providing a toner having excellent low-temperature fixing property and blocking resistance. However, pigment dispersibility, etc. is not studied, and the problem of color reproducibility is not solved. Also, in JP-A No. 62-28075, a polyester resin (resin A) is used as a binder resin, and a pigment is coated in advance with a polyester resin (resin B) having a higher molecular weight than resin A, and a color toner is obtained by dispersing this coated pigment in resin A. However, there is no disclosure regarding a crystalline resin.